Conventionally, speech and data are transferred in a circuit-switched network by allocating a dedicated channel to each connection. The dedicated channel permits to ensure certain quality and reliability. However, a problem with the circuit-switched network is that the channel is reserved for a connection, even though nothing would be transferred. In the packet-switched network a plurality of connections can share the same channel. However, since the end-users want to use familiar circuit-switched devices, these two different transmission technologies have been combined such that circuit-switched devices are used at the user end, but the actual data transmission is carried out by packet switching, for instance, using an ATM-based network. The packet-switched data transmission should be transparent to end-users and end-user applications, such as telephone traffic, ISDN (Integrated Service Digital Network), voice-band data and fax. The end-users require the same reliability and quality of service as when the circuit-switched network is used alone. To this end, various protocols have been standardized internationally, which support voice transfer over the ATM-based network, for instance. ATM Forum's ‘Loop Emulation Service Using ATM adaptation layer type 2’, or more briefly, ‘LES Using AAL2’ is one example of these standards.
However, there is a problem that current standards do not include all requirements and needs of service aware transport, such as control of codecs and echo cancellation. For instance, ELCP (Emulated Loop Control Protocol) defined in LES specifications allows exchange of channel allocation messages and user port control messages between an interworking function CP-IWF in an access device of the end-user and an interworking function CO-IWF in a gateway at the other end of the ATM network. However, these messages are not able to signal more detailed information on the state of the network or free capacity between CP-IWF and CO-IWF, for instance. In other words, they are not able to convey information on which capabilities the channel should have at any given time. This information is needed, however, in order that the user could be provided with the reliability and quality of the circuit-switched network.